Daria Kasatkina saved two match points before knocking Johanna Konta out of the Dubai Tennis Championships and Jelena Ostapenko bowed out in the second round on Wednesday.
Seventh seed Konta won the opening set and had two opportunities to reach the quarter-finals in a second-set tie-break, but went down 4-6 7-6 (8-6) 6-2 to Russian Kasatkina.
Kasatkina lost the first two games of the second set, but was back on serve at 3-3 and hung in there in the breaker before grasping her first chance to level the match.
The unseeded 20-year-old won five games in a row to move into the last eight and will now come up against compatriot Elena Vesnina.
Vesnina claimed the scalp of fourth seed Ostapenko, the French Open champion losing 6-1 7-6 (8-6).
Ostapenko lost her first match in the Qatar Open last week after being given a bye into the second round and it was the same story in Dubai, where she was broken five times.
Former world number ones Angelique Kerber and Karolina Pliskova will meet in the quarter-finals after seeing off Sara Errani and Carla Suarez Navarro respectively.
Kerber eased to a 6-4 6-2 victory over the experienced Italian, while Pliskova came from a set down to defeat Suarez Navarro 5-7 6-2 6-4. Top seed Elina Svitolina, Garbine Muguruza, Caroline Garcia and Naomi Osaka also made it through.
Top seed Dominika Cibulkova eased into the second round of the Hungarian Ladies Open with a 6-3 6-3 win over Fanny Stollar.
Defending champion Timea Babos also made progress in Budapest, thrashing Tatjana Maria 6-1 6-0 and second seed Zhang Shuai beat Arina Rodionova 6-3 6-2.
Seeds Mihaela Buzarnescu and Aliaksandra Sasnovich were dumped out by Alison Van Uytvanck and Petra Martic respectively.
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